Implement convenience move_joint script.

[adolfo-rt]

In another project, we have developed a convenience command-line tool called move_joint that allows to easily move a joint to a given position, optionally specifying the motion duration. Considering the current state of play_motion, it should be straightforward to reimplement this tool as a Python script that leverages play_motion.

The script will need to use functionality from the motion_planning branch, so it will be implemented there.

[adolfo-rt]

Noteworthy improvements over the existing implementation are:

• A lot less code overlap between the two projects.
• Use of the action interface of the joint_trajectory_controller (not the topic interface).
• move_joint is aware of the execution result, so we know if the motion succeeded or not.
• move_joint is now preemtible, i.e., ctrl-c will immediately abort execution of the current goal.
• If execution time is not specified, it's auto-computed (by play_motion) instead of defaulting to 5s.

[po1]

Has this been merged as part of #36?

[adolfo-rt]

Yes